1. Field of the Invention
This invention relates in general to Fibre Channel networks, and more particularly to a method, apparatus and program storage device for verifying existence of a redundant Fibre Channel path.
2. Description of Related Art
As computers and peripheral devices continue to improve in performance and capability, the limitations imposed by traditional parallel interfaces are becoming more apparent. Higher performance processors demand higher throughput of systems. Hardware is advancing to address this demand, but the interfaces used currently cannot ultimately keep up. To solve the problem, serial interfaces such as Fibre Channel are beginning to be designed into hardware. With higher data transfer rates, Fibre Channel offers ample performance for current as well as future demands.
Fibre Channel is a high performance, serial interconnect standard designed for bi-directional, point-to-point communications between servers, storage systems, workstations, switches, and hubs. It offers a variety of benefits over other link-level protocols, including efficiency and high performance, scalability, simplicity, ease of use and installation, and support for popular high-level protocols.
Fibre channel employs a topology known as a “fabric” to establish connections between ports. A fabric is a network of switches for interconnecting a plurality of devices without restriction as to the manner in which the switch can be arranged. A fabric can include a mixture of point-to-point and arbitrated loop topologies.
In Fibre Channel, a channel is established between two nodes where the channel's primary task is to transport data from one point to another at high speed with low latency. The Fibre channel switch provides flexible circuit/packet switched topology by establishing multiple simultaneous point-to-point connections. Because these connections are managed by the switches or “fabric elements” rather than the connected end devices or “nodes,” fabric traffic management is greatly simplified from the perspective of the device.
In a high availability, Fibre Channel switching environment, a second set of “redundant” elements are provided in the event of a failure condition. The number and make-up of the redundant elements parallel the primary elements, and operate as back-up resources if the primary elements fail. As such, in the event of such a fail condition, a switchover to the redundant elements can greatly minimize the loss of transmitted data frames.
Most modern computer networks, including switched and arbitrated-loop fibre-channel networks, are packet oriented. In these networks, data transmitted between machines is divided into chunks of size no greater than a predetermined maximum. Each chunk is typically packaged with a header and a trailer into a packet for transmission. In Fibre-Channel networks, packets are known as Frames.
A Fibre-Channel network having at least one switch is a switched Fibre-Channel fabric. A Fibre-Channel switch is a routing device generally capable of receiving frames, storing them, decoding destination information from headers, and forwarding them to their destination or another switch further along a path toward their destination. A network interface for connection of a machine to a Fibre Channel fabric is known as an N_port, and a machine attached to a Fibre-Channel network is known as a node. Nodes may be computers, or may be storage devices such as RAID systems. An NL_port is an N_port that supports additional arbitration required so that it may be connected either to a Fibre Channel Fabric or to a Fibre Channel Arbitrated Loop, and an L_port is a network interface for connecting a node to a Fibre Channel Arbitrated Loop.
A device including an N_port, L_port, or an NL_port together with hardware for high-speed connection to a machine is a Fibre Channel host bus adapter (physical HBA). For example, a physical HBA may comprise a printed circuit card having one or more NL_ports communicating through a PCI bus interface to an edge connector for connection to a PCI bus of a machine. A physical HBA may, but need not, also incorporate a processor for controlling its ports and its connection to the machine.
A Fibre Channel Switched Fabric may connect one or more Fibre Channel Arbitrated Loops. In a switched Fibre Channel fabric, there may be more than one possible path, or sequence of links, loops, switches, routers, etc. that may be traversed by a frame, between two nodes. Multiple paths may be intentional, providing extra capacity or redundancy to protect against switch, node, or line failures, or may be unintentional consequences of network topology.
Multiple paths between two nodes may also be provided through multiple Fibre Channel arbitrated loops. For example, an initiator node may have two NL_ports, one connected to each of two Fibre Channel arbitrated loops. If each of these loops connects to an NL_port of a target node, then multiple paths from the initiator to the target node exist. This could provide redundancy should a failure occur on one of the arbitrated loops.
As nodes, switches, and links are added to or removed from the network, any local topology database must be updated to reflect valid devices on the network, and valid paths through the network to those devices. Nodes also may determine one or more paths of the valid paths to a given device to be an “active” path. An active path is a path that may be used for exchanges.
The Fibre Channel specifications define Class 1 and Class 4 services to be virtual-circuit, or connection, based services between pairs of nodes. Packets of a given sequence in these services must arrive in-order with respect to other packets of the same sequence. The specifications presume that frames transiting between nodes of each pair follow a virtual circuit between the nodes—all following the same path through the network from node to node and arriving in-order.
Links, loops, and switches of a network may fail. Fibre channel networks may provide more than one path between a pair of nodes. Multiple, redundant, paths provide redundancy to allow continued communications between a pair of nodes should one or sometimes more, but not all, links, loops, or switches, and therefore paths through the network, fail.
Fibre Channel (FC) devices are identified by Nodes and their Ports. Fibre Channel requires each Port to have an unchangeable World Wide Port Name (WWPN). Fibre Channel specifies a Network Address Authority (NAA) to distinguish between the various name registration authorities that may be used to identify the WWPN. Fibre Channel identifies each Node with an unchangeable World Wide Node Name (WWNN). However, in a single port Node, the WWNN and the WWPN may be identical.
One method of providing redundant Fibre Channel connectivity is to provide a mechanism to move World Wide Node Names (WWNN) and World Wide Port Names (WWPN) from one physical interface to another in the event that the original location fails to function or can no longer be reached. However, if the path being used for Fibre Channel communication is lost, connectivity can only be restored if the source of the original connection can access the physical interface where the WWNN and WWPN are moved.
It can be seen then that there is a need for a method, apparatus and program storage device for verifying existence of a redundant Fibre Channel path.